Fire detector

ABSTRACT

A fire detector has a diphragm within a chamber and an air passage between the chamber and the ambient within which the fire detector is mounted so as to allow air flow at a predetermined rate. The fire detector has electrical contacts arranged beneath the diaphragm so that an increase of air pressure against the diaphragm causes the diaphragm to move against the contacts and to close the same. Thus, the fire detector is capable of responding either to a rate of rise of temperature faster than a predetermined rate, or to a temperature higher than a predetermined temperature. The diaphragm - which is a polyimide film material - overlies a ridge near its periphery and is secured thereto by a gasket overlying the periphery of the diaphragm and co-operating with the ridge so as to secure the diaphragm. A bushing screw having a bore axially formed therein is threaded into the air passage, and air flow from the air chamber is determined by the size of the bore in the bushing screw. Re-calibration is accomplished simply by replacing the bushing screw with one having a different sized bore.

Unite States Patent [191 Duggan 1451 July 30, 1974 FIRE DETECTOR [75] Inventor: Jack Duggan, Willowdale, Ontario,

Canada [73] Assignee: Fire Devices Manufacturing Limited,

Willowdale, Ontario, Canada OTHER PUBLICATIONS Bulletin H-lA, DuPont KAPTON, Polyimide Film, June 22, 1970, pages l, 2 & 3.

Primary Examiner-Harold Broomc 5 7] ABSTRACT A fire detector has a diphragm within a chamber and an air passage between the chamber and the ambient within which the fire detector is mounted so as to allow air flow at a predetermined rate. The fire detector has electrical contacts arranged beneath the diaphragm so that an increase of air pressure against the diaphragm causes the diaphragm to move against the contacts and to close the same. Thus, the fire detector is capable of responding either to a rate of rise of temperature faster than a predetermined rate, or to a temperature higher than a predetermined temperature. The diaphragm which is a polyimide film material overlies a ridge near its periphery and is secured thereto by a gasket overlying the periphery of the diaphragm and co-operating with the ridge so as to secure the diaphragm. A bushing screw having a bore axially formed therein is threaded into the air passage, and air flow from the air chamber is determined by the size of the bore in the bushing screw. Re-

calibration is accomplished simply by replacing the bushing screw with one having a different sized bore.

3 Claims, 4 Drawing Figures 1 FIRE DETECTOR FIELD OF INVENTION This invention relates to improvements in fire detector devices and components therefor. More particularly, this invention provides a fire detector apparatus having an improved diaphragm construction for ease of calibration, freedom from failure and a wide operating range.

BACKGROUND OF THE INVENTION Fire detector devices may be designed to function on the occurrence of at least one of two conditions, the first condition being when the rate of rise of temperature of the ambient atmosphere exceeds a certain predetermined amount for example, l5F per minute, the standard set by both the Underwriters Laboratories of Canada and the Underwriter Laboratories Inc. of the United States and the second condition being when the ambient temperature exceeds a predetermined fixed temperature. Upon the occurrence of either of these conditions, the fire detector device closes a circuit and thereby actuates an alarm. To accomplish this result, many different fire detector devices have been provided, one of which is disclosed in I. L. Seeley Canadian Patent No. 753,714, issued Feb. 28, l967, [U.S. Pat. No. 3,27 l ,547, issuedSept. 6, l966] whereby a diaphragm is used to close the circuit when either of the conditions occurs.

While it is practical both technically and economically to provide a device which responds to the occurence of either of the conditions described above, devices responding to only one of the conditions may be manufactured. Therefore, although the present invention is discussed hereafter with respect to a device which responds when either of the conditions occur; it

will be understood that where the present invention may be adapted to fire detectors which are set to respond to the occurence of only one of the conditions, the present invention is also applicable thereto.

A fire detector device usually comprises an outer shell and a head to which the outer shell is attached, with an air chamber being formed therebetween. In operation, the device usually absorbs heat through means which are exterior of the outer shell and which are disposed in the ambient atmosphere of, for example, a room. The heat is transmitted to means in the chamber of the detector device, which means will react at a predetermined temperature to close a circuit and actuate an alarm. Also, the heat absorbed by the shell of the device as well as heat transmitted to it from the exterior means will cause the air in the chamber to expand and escape out apertures in the head, which are calibrated to permit escape of a predetermined amount of air per minute. If the heated air cannot all escape, it will then cause an alarm to be actuated. The device taught in Canadian Letters Patent No. 753,714, provides a diaphragm which may be moved either by expanded air or by a detent member into a circuit closing arrangement to actuate the alarm upon the occurence of either of conditions discussed above. Suitably dimensioned apertures are provided in the head to permit for normal expansion and contraction of the air within the chamber.

The present invention may be adapted to other structures for example, the structure taught in US. Pat.

No. 2,420,775, issued May 20, 1947 although the invention is particularly discussed with reference to the structure of a first detector device as taught in the aforementioned Canadian Letters Patent No. 753,714, which utilizes a shell and also a heat collector plate to collect the heat from the outer periphery. Such a fire detector device thereby includes a heat conducting metal, to enhance the operation of the device when the rate of rise of temperature being sensed exceeds a certain predetermined calibrated setting. In accordance with the present invention, the head in which the diaphragm is mounted, as will be described hereinafter together with the aperture for regulating the rate of rise functioning of the device is preferably made of a plastic material, and in particular, a phenolic resin. The side of the head on which the diaphragm is mounted preferably comprises a vertically disposed outer wall, a concentrically disposed annular trough interiorly thereof and adjacent thereto, a ridge which is shorter than the outer wall and which is disposed interiorly of the trough and concentric therewith, and a central area in which the circuit closing means is disposed. The structures of the prior art provided a diaphragm disposed in the head and a detent means which struck the diaphragm thus closing the circuit when a predetermined temperature had been reached.

According to the present invention, an improved fire detector apparatus is provided having an improved diaphragm and a preferred disposition within the apparatus. Improved means are provided to regulate the bleeding or escape of air from the chamber between the shell and the head at a predetermined rate when the air in the chamber has been heated, so that the fire detector device will not operate when normal temperature rises are sensed.

Referring specifically to the diaphragm, heretofore diaphragms have been constructed of a thin disc of metal, particularly aluminum. However, if the metal diaphragm is creased, poor calibration of the device re sults. To avoid creasing the diaphragm, extra care must be taken, thereby requiring more time to assemble the device and thereby increasing costs of manufacture. Further, in extreme cases and because of the ambient conditions in which a prior art fire detector device has been located, holes may develop in the diaphragm of the device, which may result in a useless device. Unless a catastrophe results or unless such prior art fire detector devices are inspected regularly such failure as discussed above cannot be easily found.

Prior art fire detectors incorporating the ability to alarm when a predetermined rate of rise has been exceeded, have an opening through the head comprising a tube of restricted diameter between that portion of the heat nearest the diaphragm and the opposed side of the head which opens into a well. This well is usually pre-threaded to facilitate the insertion of a bushing screw to control the rate of escape of the air from the chamber, and thereby to calibrate the fire detector device. To calibrate, a foam is usually inserted into the well and then the bushing screw is turned therein. For final calibration of a prior art fire detector device, ma chinery known to a person skilled in the art is used. However, problems arise since the device at a future date must be recalibrated. It has been noted that in the prior art construction, the well was internally prethreaded. However, the bushing screw when screwed into the well does not necessarily follow the prethreading, but may tend to follow its own path. Usually, the top of the bushing screw is knurlled so that when the bushing screw is fully seated in the well in a desired calibrating position, the knurlling which grips into the material of the base of the well so as to securely maintain the bushing screw in place. If, however, the bushing screw has been seated too deeply and must subsequently be turned outwards, an improper calibration results since the bushing screw can no longer be secured in place by the knurlling. Furthermore, if at a future date the device is recalibrated and the screw removed from the well and possibly replaced, the well may be scored so that when another screw is inserted and fastened, the screw can not be securely maintained in the well. Therefore, the construction of the prior art I devices does readily provide for recalibration, or assure maintenance of a calibration setting once it is achieved.

On the other hand, if the well is not prethreaded to facilitate the entry of the bushing screw thereinto, then the bushing screw may not advance into the well satisfactorily. Often the well may crack because of the force required to insert the screw, and thereby faulty calibration results.

BRIEF SUMMARY OF THE INVENTION It is an object of the present invention to provide an improved fire detector device which can be manufactured at a reduced cost when compared to prior art devices and which has an increased effectiveness or efficiency of operation.

It is a further object of this invention to provide an improved diaphragm assembly for a fire detector device which can be easily handled, thereby reducing the chances of creasing the diaphragm.

A further object of this invention is to provide a diaphragm for a fire detector device at a minimal cost but having exceptionally reliable performance over a wide range of tempertures, e.g. 200C to 400C.

A still further object of this invention is to provide a more reliable fire detector device which operates at a predetermined rate of rise of temperatire, and which can be assembled in less time and at less cost than prior art devices.

Yet another object of this invention is to provide a fire detector apparatus which may be calibrated periodically without reducing the reliability thereof.

BRIEF DESCRIPTION OF THE DRAWINGS These and other objects and advantages of the invention are described hereafter in association with the accompanying drawings, in which:

FIG. 1 is an exploded, perspective view of a fire detector device of the present invention, particularly showing the improved diaphragm;

FIG. 2 is a partial cross section to a large scale, taken in the direction of lines II-II of FIG. 1;

FIG. 3 is a plan view taken in the direction of lines DESCRIPTION OF THE PREFERRED EMBODIMENT In accordance with this invention, a fire detector device is provided having an improved diaphragm and having an improved aperture calibrated forrelease of 4 heated air in the air chamber of the device, wherein the diaphragm comprises a polymeric material rather than metal. It has been discovered that not all polymeric material is satisfactory; but is preferably one that is exceptionally strong and thermally resistant, with high dielectric strength, tensile strength, flexibility, cut through resistance and resistance to cold flow, over a wide temperature range. In addition, the material should be self extinguishing, and without melting characteristics at about 750C; and it should be one that does not dissolve or craze in organic solvents, and that has high energy radiation resistance. Polyimide film materials. such as Du Pont Kapton film are particularly useful.

Referring to FIG. 1, the fire detector device of the present invention generally comprises a cup shaped shell '1 having a heat absorbing or collecting plate 2. Both shell 1 and plate 2 are made of heat conducting metal. A detent member is situated within shell 1 in the well known manner, and is set to be released at a predetermined temperature to contact the diaphragm, as discussed hereafter. A head 3 has an annular outer wall 4, with an outer diameter at surface 5 substantially equal to the inner diameter of the cup shaped shell 1. An air chamber is formed between the shell 1 and head 3 when they are assembled together. The outer wall 4 may be bevelled as at- 6 to assist assembly of the shell 1 and head 3. Concentrically disposed with the outer wall 4 is an interior adjacent trough 13, which is of less diameter than the inner diameter of wall 4. Also concentrically disposed with wall 4 and trough 13 is an inner wall or ridge 7. Each of the wall 4, trough l3 and ridge 7 is conveniently molded with head 3. Interiorly of ridge 7 there is a surface 14 in which there is formed a recess 16 in which electrical contacts generally shown at 8 may be mounted.

The diaphragm 9 preferably comprises a polyimide film material, which is exceptionally strong and thermally resistant. The diaphragm 9 has a greater diameter than the ridge 7, and when placed on ridge 7, the diaphragm projects beyond it. A gasket 10 has about the same outer diameter as diaphragm 9, and has a width substantially equal to the horizontal distance between the outer surface 11 of ridge 7 and the inner surface 12 of outer wall 4. Apertures 15 are provided through the upper surface of outer wall 4 for the passage of air therethrough so as to accommodate normal air expansion within the air chamber formed when shell 1 is assembled to head 3, under normal temperature changes It should be noted that the diaphram is disposed such that it will not be too taut to prevent it from flexing properly as required, and so that it is not too loose so as to wrinkle or dimple. If the diaphram is too loose when the fire detector device is calibrated, the diaphram may tend to move from side to side, or waves will be created therein, which may result in improper calibration.

To mount the diaphram after electrical contacts 8 are in place, the diaphram 9 is placed over the upper surface of annular ridge 7 and the gasket 10 is disposed at its periphery. The gasket 10 is then pushed into the trough 13 between surfaces 11 and 12. Preferably, a tool having the appropriate dimension to push gasket 10 into trough 13 is used; and at the same time, the tool assures that the diaphragm is advanced towards contacts 8. The trough 13 is preferably tapered from its top to its bottom as seen in FIG. 2, so that a frictional fit is obtained between the gasket and the surfaces 11 and 12 as the diaphram 9 extends over the ridge 7 and above the trough 13. Thus, when the gasket is pushed into the trough l the diaphram is effectively secured in place. To further secure the diaphram in place an epoxy may then be poured into the trough 13 above the gasket 10 and allowed to cure, thus firmly securing the diaphram 9 in place. The diaphragm is of an appropriate thickness, generally about 0.0025 inches.

To permit recalibration of the fire detector device without firstly affecting satisfactory use of the device, an improved aperture construction is provided whereby the device can be recalibrated as desired. Aperture 15 has its upper end at the upper surface of outer wall 4. The aperture 15 communicates through a tube 30 and a well 31 to the under side of the head 3, as particularly shown in FIG. 2. The well 31 is vertically splined as at 32 as shown in FIGS. 2 and 3 and foam material 50 may or may not be inserted into the well 31. A bushing screw 40 having helical threads 43 thereon, is driveable at recess 41 by insertion of a screw driver, Allen bit or other suitable device. The bushing screw is preferably unknurlled. The bushing screw 40 is further preferably provided with a fine thread pitch as indicated at 41; so that if it is turned into the well 31 and the spline 32 thereof and then removed and returned into the well, the earlier formed thread in the splines 32 is of minimal effect. The bushing screw 40 contains a bore 45 axially formed therein, to permit air to flow through the bushing screw after it has passed through foam 50 from tube 30, at a predetermined airflow rate. The fire detector device may be easily recalibrated to operate at a different rate-ofrise of temperature merely by replacing the bushing screws 40 with others having a different bore size, and thus a different maximum air-flow rate.

In operation, if the air entrapped within the air chamber between the upper surface of diaphragm 9 and the inside of shell 1 cannot escape through calibrated apertures 15 fast enough, then the air pressure which is thereby created, forces the diaphragm 9 into operating engagement with electrical contacts 8; and if the pressure increases sufficiently, the conacts close and the device operates in the intended manner. Thus, the rate of flow of air through apertures 15 is controlled by the setting of bushing screws 40 in wells 31, and the rate of temperature rise which causes the electrical contacts 8 to close is thereby established.

It should be noted that assembly of a fire detector device in accordance with this invention may be easily and inexpensively achieved, in minimum time and without adjustments except for calibration of the temperature rate-of-rise operation. By suitable dimensioning, a ridge, gasket and diaphragm in accordance with this invention may be applied to prior art fire detector apparatus; and because of the manner of installation of the diaphragm, initial calibration of the rate-of-rise operation of the device may be reasonably predicted and duplicated.

Many modifications and alterations can be made to the fire detector device of the present invention without departing from the spirit and scope of the appended claims.

What I claim is:

1. in a fire detector device having a head, a shell adapted to fit over said head so as to form an air chamber therebetween, and a diaphragm within said air chamber; at least one air passage between said air chamber and the ambient within which said fire detector device is installed, to allow air to flow from said air chamber at a flow rate up to a predetermined air flow rate; electrical contacts arranged beneath said diaphragm so that upon an increase of air pressure within said air chamber, said diaphragm is forced against said electrical contacts to close the same; said diaphragm comprising a polyimide film material overlying a ridge near its periphery, and being secured thereto by a gasket overlying the periphery of said diaphragm and in co-operating relation with said ridge to secure said diaphragm between the outer side of said ridge and said gasket;

said at least one air passage having threadably engaged therein a bushing screw which has a bore of predetermined size axially formed therein, so as to permit air flow from said air chamber through said air passage and said bore to the ambient, at a predetermined flow rate;

said at least one air passage comprising an aperture in said head in communication with said air chamber and a well disposed in said head at the opposed end of said air passage to said air chamber, said well being splined to accommodate and secure said bushing screw.

2. The combination of claim 1 where the diaphragm is about 0.0025 inches in thickness.

3. The combination of claim 1 further comprising an epoxy placed over said gasket so as to further secure said diaphragm and gasket in a fixed position relative to said head. 

1. In a fire detector device having a head, a shell adapted to fit over said head so as to form an air chamber therebetween, and a diaphragm within said air chamber; at least one air passage between said air chamber and the ambient within which said fire detector device is installed, to allow air to flow from said air chamber at a flow rate up to a predetermined air flow rate; electrical contacts arranged beneath said diaphragm so that upon an increase of air pressure within said air chamber, said diaphragm is forced against said electrical contacts to close the same; said diaphragm comprising a polyimide film material overlying a ridge near its periphery, and being secured thereto by a gasket overlying the periphery of said diaphragm and in cooperating relation with said ridge to secure said diaphragm between the outer side of said ridge and said gasket; said at least one air passage having threadably engaged therein a bushing screw which has a bore of predetermined size axially formed therein, so as to permit air flow from said air chamber through said air passage and said bore to the ambient, at a predetermined flow rate; said at least one air passage comprising an aperture in said head in communication with said air chamber and a well disposed in said head at the opposed end of said air passage to said air chamber, said well being splined to accommodate and secure said bushing screw.
 2. The combination of claim 1 where the diaphragm is about 0.0025 inches in thickness.
 3. The combination of claim 1 further comprising an epoxy placed over said gasket so as to further secure said diaphragm and gasket in a fixed position relative to said head. 